A fluid dynamic bearing device is configured to relatively rotatably support a shaft member in a non-contact manner by a pressure generated by a fluid film (for example, an oil film) in a radial bearing gap defined between an outer peripheral surface of the shaft member and an inner peripheral surface of a bearing member. The fluid dynamic bearing device has advantages in high rotational accuracy and quietness. Thus, the fluid dynamic bearing device is preferably used for a spindle motor for information equipment (for example, magnetic disk drives such as an HDD, drives for optical discs such as a CD-ROM, a CD-R/RW, a DVD-ROM/RAM, and a Blu-ray Disc, and drives for magneto-optical disks such as an MD and an MO), a polygon scanner motor for a laser beam printer (LBP), a color wheel for a projector, and a small-sized motor such as a fan motor to be used for a cooling fan or the like of an electrical apparatus.
The fluid dynamic bearing device is roughly classified into a type including a radial dynamic pressure generating portion formed on the inner peripheral surface of the bearing member or the outer peripheral surface of the shaft member and configured to actively generate a dynamic pressure in the fluid film in the radial bearing gap (so-called “dynamic bearing”), and a type including the inner peripheral surface of the bearing member and the outer peripheral surface of the shaft member both formed as cylindrical surfaces and being configured to generate a dynamic pressure through whirling of the shaft member (so-called “circular cylindrical bearing”). For example, in Patent Literature 1, there is described an example of the dynamic bearing.